the heating then continued for 20-30 minutes longer. If finely powdered,
the sample should then be completely attacked.
(6) FUSION WITH SODIUM CARBONATE AND MAGNESIA. 0-3-0-5 gram of
the finely powdered sample is mixed with about 10 parts of a mixture
of sodium carbonate and magnesium oxide, and the mixture heated in a
platinum crucible under the conditions prescribed for the analysis of
Titration of the chromium. The fused mass obtained by one of the above
methods is lixiviated with water, as indicated on p. 183 (Chrome Steels),
any manganates formed being reduced with sodium peroxide, the liquid
filtered, boiled to expel excess of sodium peroxide and made up to volume
in a 500 c.c. measuring flask ; the chromium is then titrated iodometrically
on several 50 or 100 c.c. portions (see Chrome Steel).
If it is suspected that the attack of the metal has not been completed, the
residue from the lixiviation is dried, fused with sodium carbonate and the fused
mass again lixiviated, the resultant solution being added to that from the first
2. Determination of the Carbon.—This is effected by direct com-
bustion in a current of oxygen (see Iron, i, b).
3. Determination of the Manganese.—The residue obtained in the
lixiviation with water of the fused mass is dissolved in hydrochloric acid
and treated as indicated under Ferro-silicon, 3.
4. Determination of the Silicon, Phosphorus and Sulphur.—As
Ferro-chrome contains 40-65% Cr (rarely 80%), quantities of carbon vary-
ing according to the degree of refining, and the ordinary impurities found in
cast-iron. Three grades are distinguished commercially :
1. Refined ferro-chrome No. i (0-3-0-75% C, 60% Cr).
2. Refined ferro-chrome No. 2 (1-2% C, 60% Cr).
3. Ordinary ferro-chrome (4-10% C, 60% Cr).
The following table gives the mean compositions of various ferro-chromes
Composition of Ferro-chromes
8-10% of carbon
Less than i % of carboi
of 80-85° a 15% potassium chloride solution rendered